The purpose of this project is to understand motility and cytoskeleton-membrane interactions in the intracellular protozoan parasite Toxoplasma gondii. Genetic and cell biological studies have determined that parasite motility and cell invasion is powered by an actin-myosin based motor in the parasite, but it has not been possible so far to localize actin filaments with Fonventional. electron microscopy. This led to the conclusion that actin might exist primarily in globular form. T gondii represents an interesting parasite system in which to study cytoskeletal motility. Unlike bacterial cell uptake, parasite invasion does not involve significant alteration in the host cell cytoskeleton. Instead, invasion is an active process of penetration into the host cell by the parasite. During invasion, actin and myosin that is localized underneath the plasma membrane in the parasite presumably combine to produce the force necessary for motility during invasion. By using the techniques described by Dr. Ris to look at actin and myosin structures with LVSEM we expect to be able to determine the mechanisms underlying the gliding motility in the parasite T gondii and its interactions with host cells during parasite invasion.